Paint inspection



Patented June 1 1943 PAIN T- INSPECTION Charles F. Arnold and Laurence L. Kortkamp, Detroit, Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Serial No. 449,012

No Drawing. Application June 29, 1942, f

5 Claims. (Cl.-117-66) This invention has to do with the determination or the-quality of a painted or lacquered coating as regards its covering an undercoat.

One of the most diflicult production problems regarding lacquer finish concerns the detection and repair of thin spots, particularly on edges and crease lines. Detection of thin finish requires a far more rigid visual inspection under strong lights than can be expected of the average production inspector for a continuous. day's work. 1 The thin spots may occur as a. result of insufllcient paint or lacquer having been applied in the first place, or they may occur as a result of paint or lacquer being removed to such an extent in one or more places during wet sanding or other conventional smoothing operations as to produce painted or lacquered portions that are dangerously thin. Thin spots caused by sanding operations may be greater in those applications requiring higher standards of smoothness for the finished paint job. For example, in the automotive field higher priced cars at times may require an excess amount of wet sanding in orderto reduce orange peel to a minimum, whereas manufacturers of lower priced cars consider "orange peel" as part of their standard quality and make no attempt to sand it out.

The present invention is concemedwith the inspection of the finish in order to determine whether or not there are any thin spots. If

thin spots are present the finish can-then be observed and repaired before the product leaves the factory. Our invention comprises the formation of the undercoat, primer, or ground 'and 67% volatile.

invention. The fluorescent material is ground to lacquer pigment texture and reduced to spraying consistency with lacquerthinner. A typical formula consists of 14% pigment. 19% vehicle, The ratio is 19 ounces of pigment by weight per gallon. Tests indicate that about 4 ounces per gallon of this mixture will fluoresce brilliantly regardless of the'opaque The thin spots in the center of the panel were the panel was exposed to ultra-violet filtered light the thinareas and thin edges fluoresced brilliantly and could be detected instantly.

The test procedure was repeated using standard black lacquer as a vehicle instead of Shetland gray. The results were the same as in the previous example except that the brilliance boat with a small amount of a fluorescent or luminescent material, and the inspection of the finished surface under light which'includes components of the correct wave length to produce luminescence. or fluorescence of the undercoating. Fluorescent materials are not visible under ordinary sunlight or Mazda type lamps and are radio-active only when excited by direct Zinc sulphide is illustrative of a fluorescentmaterial that has been used in carrying out the of the fluorescent material was about 30% lessdue to the opaqueness of the black lacquer pigment.

, Various changes may be made in the embodiment of our-invention disclosed herein without departing from the principles of our invention and we do not intend to limit the patent granted for our invention except asnecessitated by the prior art.

We claim:

1. The method, of determining the quality of thin portions in the coating to be tested are readily visible.

2. The method of determining the presence of thin spots in a painted or lacquered surface which includes applying an undercoat containing a small amount. of a fluorescent material, covering the undercoat with a layer of paint or lacquer, and subjecting the composite coating to the action of ultraviolet light whereby any thin .spots in the covering layer of paint or lacquer ing a small amount of zinc sulphide, applying to the ground coating one or more layers of paint or lacquer, and subjecting the composite coating to the action of ultra-violet light whereby any thin spots in the exterior paint or lacquer are readily visible due to the excitation of the fluorescent material in the ground coat 4. The method of painting or lacquering and determining the presence or lack of thin spots therein which includes applying an .undercoat containing a fluorescent material, applying one or more layers of paint or lacquer to the .under-' coatQsubiecting the paint or lacquer coating to conventional sanding or smoothing operations, and inspecting the coating under ultra-violet light whereby any thin spots in the paint or lacquer are readily visible due to the excitation of the fluorescent material in the undercoating.

5. The method of determining the presence of thin spots in, a painted or lacquered surface which includes, applying a ground coat containing a fluorescent material, covering said ground coat with a coating of paint or lacquer, and subjecting the lacquered surface to light rays which activate the fluorescent material whereby any thin spots in the lacquered coating are readily visible.

CHARLES F. ARNOLD. LAURENCE L. KOR'I'KAMP. 

